With the current popularity of portable communication devices and developed semiconductor fabrication technology, high speed and high performance transistors are more densely integrated on semiconductor dies. The amount of heat generated by the semiconductor dies increases significantly due to the growth in number of transistors per semiconductor die, the growth of power passing through the transistors, and the growth of operation speed of the transistors. If the heat generated by the semiconductor dies cannot be dissipated efficiently, the semiconductor dies may fail to operate or have a degraded operating performance. Normally, semiconductor dies reside in or on a bulk substrate, and the bulk substrate can affect the semiconductor dies performance in many ways. For instance, the heat produced by the semiconductor dies could be conducted away from their immediate vicinity through the bulk substrate. Accordingly, metal-diamond composites, which have superior thermal conductivity, are introduced to form the bulk substrate. In addition, metal-diamond composites present advantages to semiconductor packaging in that the coefficient of thermal expansion (CTE) is within the acceptable region for use with semiconductor devices.
A major challenge with the metal-diamond composites is, after dicing the bulk substrate into individual substrates, at least the sidewalls of each substrate present surfaces including both electrically conductive metal and electrically non-conductive diamond. Therefore, electroless plating is the only option for protecting these sidewalls. Electroless nickel plating is a conventional technique used to deposit a coating of nickel on a substrate to prevent corrosion and wear. However, the electroless nickel plating is relatively brittle and has a relatively large CTE mismatch to the metal-diamond composites. The electroless nickel plating may crack during temperature cycle (between −65° C. and 150° C.), and may cause failure during corrosive environment exposure such as salt fog.
Accordingly, there remains a need for improved substrate designs, which could utilize the thermal advantages of the metal-diamond composites, and reduce the brittle and/or CTE mismatch disadvantages from the electroless nickel plating. The substrate designs will also preferably be low cost and use easily attainable materials.